The present invention relates to an optical pickup apparatus suitable for use with optical video disk players, compact disk players, optical disk systems, magnetooptical recording and reproducing apparatus, etc.
In reproducing recorded information from the disk of an optical video disk player, laser light emitted from a light source such as a semiconductor laser is focused at a point on the disk and tho light reflected from the illuminated disk is picked up. The reflected light is modulated by the information recorded on the disk, so that by performing photoelectric conversion on this light, an electric signal corresponding to the recorded information can be obtained.
For correct reproduction of the recorded information from the disk, it is necessary that light be not only focused on the surface of the disk where information is recorded but also caused to closely follow the track on which the information of interest is recorded. To meet this need, an optical pickup apparatus is equipped with a mechanism by which the objective lens for converging light onto the disk is driven both in a direction perpendicular to the disk (focusing direction) and in a radial direction (tracking direction). While this drive mechanism is available in various designs, the usual type is such that a magnet is combined with a yoke to form a closed magnetic circuit, with a tracking and a focusing coil being placed within the magnetic field of the magnetic circuit and supplied with associated error signals.
In the prior art optical pickup apparatus, the tracking and focusing coils are wound one on top of another so that both are driven by a common magnetic circuit. Thus, in order to ensure that the tracking coil will not contact either the top or bottom surface of the yoke during driving in a focusing direction, the distance between the tracking coil and the yoke must be made adequately large in the focusing direction, but then the apparatus will increase in size, particularly in height, or thickness.